A series of rigid rod amide monomers based on 2,2′‐disubstituted‐4,4′‐diaminobiphenyl were prepared and characterized by DSC and hot stage polarized light microscopy. The monomers were endcapped with maleimide, nadimide, and methylnadimide functionalities. With one exception, all of the materials could be thermally polymerized. Nematic liquid crystalline behavior was observed in three of the new materials which could be crosslinked in either the nematic or isotropic phase. Fast heating rates with hot stage polarized light microscopy were necessary to determine the melting and phase behavior before substantial crosslinking occurred during the heating process. One of the methylnadimide endcapped monomers also showed lyotropic liquid crystalline behavior.
Nine rigid rod ester monomers endcapped with maleimide, nadimide, and methylnadimide groups were prepared and studied by DSC and hot stage polarized light microscopy. All of the monomers showed thermotropic nematic liquid crystalline phases and could be thermally crosslinked in the nematic phase. The nematic texture was maintained in the crosslinked solid state. The nematic phase range was enlarged by B‐staging the monomeric compounds. Heating the monomers for a short period of time in the nematic phase lowered the crystal to nematic transition temperatures and increased the nematic to isotropic transition temperatures. A nonequilibrium phase diagram was proposed to explain the melting behavior of these reactive liquid crystal thermoset materials.
SYNOPSISAmine-terminated and maleimide-terminated oligomers of molecular weight 1200-1800 based on 2,2'-bis(trifluoromethyl)-4,4'-diaminobipheny1 and 3,3',4,4'-biphenylenetetracarboxylic dianhydride were synthesized and characterized for lyotropic liquid crystalline behavior. Several different synthetic procedures were evaluated and a one-step procedure in rn-cresol was found to be the most effective for producing fully imidized materials. Lyotropic behavior was observed only for the as-prepared solutions in rn-cresol and in dilutions of this solution. Oligomer thermal stability was excellent, onsets of decomposition were in excess of 550°C. 0 1996 John Wiley & Sons, Inc. Keywords: lyotropic liquid crystalline behavior reactive oligomers polyimide one-step polyimide synthesis
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